<!DOCTYPE html><html lang="zh-Hans"><head><meta charset="UTF-8"><meta http-equiv="X-UA-Compatible" content="IE=edge"><meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1"><meta name="description" content="runtime方法交换"><meta name="keywords" content="runtime,小书匠"><meta name="author" content="kyren"><meta name="copyright" content="kyren"><title>runtime之方法交换 | Kyren's Blog</title><link rel="shortcut icon" href="/melody-favicon.ico"><link rel="stylesheet" href="/css/index.css?version=1.9.0"><link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/font-awesome@latest/css/font-awesome.min.css?version=1.9.0"><meta name="format-detection" content="telephone=no"><meta http-equiv="x-dns-prefetch-control" content="on"><link rel="dns-prefetch" href="https://cdn.jsdelivr.net"><link rel="dns-prefetch" href="https://hm.baidu.com"><script>var _hmt = _hmt || [];
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<span id="more"></span>

<h2 id="原理简介："><a href="#原理简介：" class="headerlink" title="原理简介："></a>原理简介：</h2><p>方法交换，顾名思义，就是将两个方法的实现交换。例如：将A方法和B方法交换，调用A方法的时候，就会执行B方法中的代码，反之亦然。<br> 1.SEL – 表示该方法的名称又名选择器；<br> 2.types – 表示该方法参数的类型；<br> 3.IMP – 指向该方法的具体实现的函数指针，也就是就是实现方法。<br>参考：<a target="_blank" rel="noopener" href="http://nshipster.com/method-swizzling/">http://nshipster.com/method-swizzling/</a></p>
<h2 id="新建Category文件"><a href="#新建Category文件" class="headerlink" title="新建Category文件"></a>新建Category文件</h2><p><code>UIViewController+SwizzleMethods.h</code></p>
<figure class="highlight objectivec"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">//  UIViewController+SwizzleMethods.h</span></span><br><span class="line"><span class="comment">//  RuntimeLearn</span></span><br><span class="line"><span class="comment">//</span></span><br><span class="line"><span class="comment">//  Created by luo.h on 16/3/3.</span></span><br><span class="line"><span class="comment">//  Copyright © 2016年 appledev. All rights reserved.</span></span><br><span class="line"><span class="comment">//</span></span><br><span class="line"></span><br><span class="line"><span class="meta">#import <span class="string">&lt;UIKit/UIKit.h&gt;</span></span></span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">@interface</span> <span class="title">UIViewController</span> (<span class="title">SwizzleMethods</span>)</span></span><br><span class="line"></span><br><span class="line"><span class="keyword">@end</span></span><br></pre></td></tr></table></figure>

<p><code>UIViewController+SwizzleMethods.m</code></p>
<figure class="highlight objectivec"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">//</span></span><br><span class="line"><span class="comment">//  UIViewController+SwizzleMethods.m</span></span><br><span class="line"><span class="comment">//  RuntimeLearn</span></span><br><span class="line"><span class="comment">//</span></span><br><span class="line"><span class="comment">//  Created by luo.h on 16/3/3.</span></span><br><span class="line"><span class="comment">//  Copyright © 2016年 appledev. All rights reserved.</span></span><br><span class="line"><span class="comment">//</span></span><br><span class="line"></span><br><span class="line"><span class="meta">#import <span class="string">&quot;UIViewController+SwizzleMethods.h&quot;</span></span></span><br><span class="line"><span class="meta">#import <span class="string">&lt;objc/runtime.h&gt;</span></span></span><br><span class="line"></span><br><span class="line"><span class="class"><span class="keyword">@implementation</span> <span class="title">UIViewController</span> (<span class="title">Swizzle</span>)</span></span><br><span class="line"></span><br><span class="line"><span class="comment">//load方法会在类第一次加载的时候被调用 相关：http://blog.leichunfeng.com/blog/2015/05/02/objectivec-plus-load-vs-plus-initialize/</span></span><br><span class="line"><span class="comment">//调用的时间比较靠前，适合在这个方法里做方法交换</span></span><br><span class="line"><span class="comment">//注意：不要在+initialize中交换</span></span><br><span class="line"><span class="comment">//+initialize是类第一次初始化时才会被调用，因为这个类有可能一直都没有使用到，因此这个类可能永远不会被调用。</span></span><br><span class="line">+ (<span class="type">void</span>)load&#123;</span><br><span class="line">    <span class="comment">//方法交换应该被保证，在程序中只会执行一次</span></span><br><span class="line">    <span class="keyword">static</span> <span class="built_in">dispatch_once_t</span> onceToken;</span><br><span class="line">    <span class="built_in">dispatch_once</span>(&amp;onceToken, ^&#123;</span><br><span class="line">         <span class="comment">//方法交换</span></span><br><span class="line">        SwizzlingMethods([<span class="keyword">self</span> <span class="keyword">class</span>], <span class="keyword">@selector</span>(viewWillAppear:), <span class="keyword">@selector</span>(swiz_viewWillAppear:));</span><br><span class="line">    &#125;);</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line"></span><br><span class="line"><span class="comment">/** 方法交换*/</span></span><br><span class="line"><span class="type">void</span> SwizzlingMethods(Class cls, SEL systemSel, SEL newSel)</span><br><span class="line">&#123;</span><br><span class="line">    <span class="comment">//两个方法的Method</span></span><br><span class="line">    Method systemMethod = class_getInstanceMethod(cls, systemSel);</span><br><span class="line">    Method newMethod = class_getInstanceMethod(cls, newSel);</span><br><span class="line"></span><br><span class="line">    <span class="comment">//首先动态添加方法，实现是被交换的方法，返回值表示添加成功还是失败</span></span><br><span class="line">    <span class="type">BOOL</span> isAddMethod = class_addMethod(cls,systemSel,</span><br><span class="line">                                       method_getImplementation(newMethod),</span><br><span class="line">                                       method_getTypeEncoding(newMethod));</span><br><span class="line">    <span class="keyword">if</span>(isAddMethod)&#123;</span><br><span class="line">        <span class="comment">//如果成功，说明类中不存在这个方法的实现</span></span><br><span class="line">        <span class="comment">//将被交换方法的实现替换到这个并不存在的实现</span></span><br><span class="line">        class_replaceMethod(cls, newSel, method_getImplementation(systemMethod), method_getTypeEncoding(systemMethod));</span><br><span class="line">    &#125;<span class="keyword">else</span>&#123;</span><br><span class="line">        <span class="comment">//否则，交换两个方法的实现(改变两个方法的具体指针指向)</span></span><br><span class="line">        method_exchangeImplementations(systemMethod, newMethod);</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br><span class="line"></span><br><span class="line">- (<span class="type">void</span>)swiz_viewWillAppear:(<span class="type">BOOL</span>)animated&#123;</span><br><span class="line">    <span class="comment">//看起来像是死循环，但是其实自己的实现已经被替换了</span></span><br><span class="line">    <span class="comment">//防止UINavigationController 或 UIInputWindowController调用次数变多</span></span><br><span class="line">    <span class="keyword">if</span> ([<span class="built_in">NSStringFromClass</span>([<span class="keyword">self</span> <span class="keyword">class</span>]) isEqualToString:<span class="string">@&quot;UINavigationController&quot;</span>] || [<span class="built_in">NSStringFromClass</span>([<span class="keyword">self</span> <span class="keyword">class</span>]) isEqualToString:<span class="string">@&quot;UIInputWindowController&quot;</span>]) &#123;</span><br><span class="line">        <span class="keyword">return</span>;</span><br><span class="line">    &#125;</span><br><span class="line">    [<span class="keyword">self</span> swiz_viewWillAppear:animated];</span><br><span class="line">    <span class="built_in">NSLog</span>(<span class="string">@&quot;✅VC-&gt;%@&quot;</span>,[<span class="keyword">self</span> <span class="keyword">class</span>]);</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">@end</span></span><br><span class="line"></span><br></pre></td></tr></table></figure>






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